Research Paper

Dynamic control of Cajal body number during zebrafish embryogenesis

Volume 1, Issue 1   January/February 2010
Pages 96 - 108
http://dx.doi.org/10.4161/nucl.1.1.10680
Authors: Magdalena Strzelecka, Andrew C. Oates and Karla Neugebauer

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Abstract:

The Cajal body (CB) is an evolutionarily conserved nuclear
subcompartment, enriched in components of the RNA processing
machinery. The composition and dynamics of CBs in cells of living
organisms is not well understood. Here we establish the zebrafish
embryo as a model system to investigate the properties of CBs during
rapid growth and cell division, taking advantage of the ease of live-cell
imaging. We show that zebrafish embryo CBs contain coilin and
multiple components of the pre-mRNA splicing machinery. Histone
mRNA 3’ end processing factors, present in CBs in some systems, were
instead concentrated in a distinct nuclear body. CBs were present in
embryos before and after activation of zygotic gene expression,
indicating a maternal contribution of CB components. During the first
24 hours of development, embryonic cells displayed up to 30 CBs per
nucleus; these dispersed prior to mitosis and reassembled within
minutes upon daughter cell nucleus formation. Following zygotic
genome activation, snRNP biogenesis was required for CB assembly
and maintenance, suggesting a self-assembly process that determines
CB numbers in embryos. Differentiation into muscle, neurons and
epidermis was associated with the achievement of a steady state
number of 2 CBs per nucleus. We propose that CB number is regulated
during development to respond to the demands of gene expression in
a rapidly growing embryo.

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